The specific aims of the research are to: 1. Continue to characterize the acute effects of delta-9-THC on auditory evoked neural activity in the dentate gyrus of the unanesthetized behaving rat. These experiments consist of dose-response analyses of the effects of delta-9-THC on synaptically identified auditory evoked potentials and dentate granule cell single unit discharges during the performance of both simple and complex auditory discrimination tasks. 2. Initiate studies on the effects of repeated daily administration of low and high doses of delta-9-THC on auditory evoked activity in the dentate gyrus, and dentate g-cell activity during prolonged performance of the auditory discrimination task. In these experiments we will determine whether tolerance to the acute effects of delta-9-THC develops with respect to these measures following either low or high doses of the drug when given repeatedly over several days. Specialized analyses of trial-by-trial variations in amplitude of these evoked responses indicate that event related correlates of cognitive processes may be altered by high dose levels of delta-9-THC. 3. Determine the effects of withdrawal from long-term exposure to both low and high doses of THC on the auditory evoked dentate gyrus neural activity. In addition, investigations of residual effects of delta-9-THC on these neurobehavioral correlates will also be examined following prolonged exposure to very high dose levels.